1) Field of the Invention
The present invention relates to an information recording/reproducing apparatus, in which information is recorded or reproduced with the aid of an optical information recording medium such as an optical card. Particularly, the present invention relates to a tracking control technique which can be suitably applied to an information recording/reproducing apparatus having two light sources, one of which is for use in the information recording medium and the other in reproducing information recorded on the medium.
2) Description of the Related Art
In the information recording/reproducing apparatus in which information is recorded on and/or reproduced from the optical information recording medium such as an optical card, an information reading out speed is determined in accordance with a relative moving speed between an optical head provided in the apparatus and the information recording medium. Therefore, when the apparatus is arranged such that a light beam emitted from a light source is illuminated on a single track out of a plurality of tracks formed on the information recording medium to read out information recorded on the relevant track, it is difficult to make the information read out, speed up.
In U.S. Pat. No. 4,730,293, an information recording/reproducing apparatus is disclosed in which a light beam emitted from a light source illuminates a plurality of tracks simultaneously to read out information recorded on the plurality of tracks in a parallel manner, resulting in that the information reading out speed is high. The applicant also suggests a data demodulating system for reading out data recorded in a plurality of data recording areas formed on an information recording medium simultaneously; in Japanese Patent Preliminarily Publication No. Hei2-141932.
Further, in publication "High Speed Optical Card Reader/Writer Using Two Optical Sources" preliminarily documents C-325 of the All Japan Meeting of Telecommunication Society in autumn 1989, an apparatus in which information is recorded/reproduced with a high speed by using an optical head having two optical sources is published. In this apparatus, one of the optical sources is used for recording information on an information recording medium and the other one for reproducing information recorded on the information recording medium.
FIG. 1 is a schematic view showing a construction of an optical head of the apparatus published in the publication. In FIG. 1, a numerical reference 1 denotes a laser diode for emitting a light beam, which is used for recording information; 2 a collimator lens for making the light beam emitted from the laser diode 1 parallel; 3 a polarization beam splitter; 4 an objective lens; 5 an actuator for driving the objective lens; 6 a light emitting diode for emitting a light beam, which is used for reproducing information; 7 a collimator lens for making the light beam emitted from the light emitting diode 6 parallel; 8 an optical card as an optical information recording medium; 9 and 10 mirrors for changing an optical path of a reflection light beam reflected by the optical card 8; 11 an imaginary lens; 12 a beam splitter; 13 a photo detector for detecting a tracking error signal; and a numerical reference 14 represents a photo detector for detecting a focus error signal.
FIG. 2 is a schematic view representing a construction of a signal detecting system in the apparatus shown in FIG. 1 for detecting an information data signal and a tracking error signal. A numerical number 21 represents guide tracks formed on the optical card 8; 22 data pits recorded on data tracks formed between the guide tracks 21 on the optical card 8, information is recorded in the data tracks with the aid of the data pits; 23 a light beam spot of a light beam emitted from the laser diode 1 for recording information; and a numerical number 24 represents a light beam spot of a light beam emitted from the light emitting diode 16 for reproducing information. It should be noted that a numerical number 25 represents a lens system provided in the apparatus and that on the photo detector 13 for detecting the information data signal and the tracking error signal, there are provided light receiving elements 26, 26, which are for reading out information data and light receiving elements 27, 27, which are for detecting the tracking error signal.
As shown in FIG. 2, the light beam spot 23 for recording information and the light beam spots 24 for reproducing information are formed on the optical card 8 with a distance of several ten .mu.m in a track direction, which is parallel to a direction along which the guide tracks 21 are extended, so that it is possible to read out information data directly during writing. In this apparatus, since information can be verified at the same time of writing, an operating time of the system can be shortened to a half.
Further, the light beam for reproducing information illuminates the optical card 8 across over two data tracks in a tracking direction, which is perpendicular to the track direction; and images of two data tracks are formed on the light receiving elements 26, 26 for reading out information. Therefore, in the apparatus, it is possible to read out information formed on the two data tracks which can be read out simultaneously.
On the photo detector 13, between the light receiving elements 26, 26 for reading information data, are used provided the light receiving elements 27, 27 which are for detecting tracking error signal. The tracking control is conducted in the apparatus in such a manner that images formed on an upper area .gradient. and a lower area .DELTA. of the light receiving elements 27, 27 are balanced in light and shade. It should be noted that the recording of information is conducted with the aid of a light spot 23 of the light beam emitted from the laser diode 1.
However, in the information recording/reproducing apparatus explained in the above, a tracking control of the light beam for recording during when information is recorded is performed with the aid of a reflection beam of a light beam emitted from the light emitting diode 6, which is used for reproducing information. Therefore, when information is recorded in the data tracks formed on the optical card 8, the relative positional relation between the light beam spot 23 of the light beam emitted from the laser diode 1 and the light beam spots 24 of the light beam emitted from the light emitting diode 6 is important. That is to say, when the relative positional relation between the laser diode 1 and the light emitting diode 6 is varied so that the positions of members, on which these diodes 1 and 6 are provided, are varied due to a temperature variation of an atmosphere around the apparatus, the light beam spot 23 of the light beam emitted from the laser diode 1 would be shifted in upper and lower directions from the relevant guide track.
Generally, the guide tracks are formed on the optical card 8 with a distance of about several .mu.m to ten .mu.m, so that even if an amount of the variation of the relative position of the laser diode 1 and the light emitting diode 6 is very small, i.e. 1 .mu.m-several .mu.m, there is a possibility that the light beam spot of the light beam emitted from the laser diode 1 (hereinafter represented by LD spot) would be shifted from the relevant data track. When the LD spot 23 is sifted from a center of the data track, the recording pit 22 is also formed to be sifted from the center of the data track, of course; in the worst case, when reading out information data, the image of the pit 22 is deviated from the light receiving elements 26, 26 which is used for detecting information data, so information data could not be read out.
Furthermore, according to an accuracy in assembling the optical head, optical axes of light beam for recording information and light beam for reproducing information are sometimes deviated from each other. In such case, since it is necessary to adjust the deviation of the optical axes, the cost for manufacturing the apparatus would be increased and the reliability of the apparatus decreased.